Elevator control system



Patented Mut. 31 1942 2,27s120 nx.nvuon. comrnor. SYSTEM Ernst L. Schwarz, Chicago, Ill. asslxnor to Annour Beseatch Foundation, a corporatlon o! lllinols Application May 27, 1940, Serial N0. 337,331

9 Chinas.

The present. invention relates in general to the control of load raising and lowering equipmeni;

and is particularly concerned with a control system which may be advantageously applied to the control' of passenger elevators. freight e1evators,

skip hoists such es may be utilized with blast furnaces, etc., and especially equipment 015 this type wherein smoothness 01 operation, accurate landings, and maintenance of theload carrying means at a desired level during loading and unloading may be desired.

One of the most impmtanb problems in the clesign of elevators has to do with speed regulation, since the attainment of proper regulation materially lessens the subjection of the main hoisting motor, the mechanical parts, and the electrical control to undue stresses, and results in decrease of the requirecl time for making a round trip, as weil as increase and improve the service and smoothness of operation. Speed regulation is of particular importance in high-speed elevators for accurate landing wii;hout inching and for maintenance of the car level during loading and un1oading. A high degree of speed regulation is therefore desirabie, and this degre of regulation must be practically constant independent of the weight of the car load and for both up and down directions of movement of the elevator.

For alternating current installation's, there have been several systems which have come int-o general use.

One system which has been extmsively ubilized makes use of the well known Ward-Leonard control in which a motor-generator sei; is interposed between the main hoisting motor and Ehe system from which it is supplied. 'Ihis system is particularly advantageous for elevators due to i ts excellent speed regulation. -iiny desired varia(sion in the speed of the hoisting motbr may be effected. This equipment, however, is objectionable in that it is not only expensive, but requires additional space for installation of the motorgenerator sets. Each elevator motor requires a separate motor-generator sei: of fu1l capacity for the hoisting motor and also a reserve motor-generator set for emeraency use. Moreov'er, the motor-generator sets mustbe kept running, whether o1 not the elevator motors are being operated. Therefore, the relative high p0wer consumption for stand-by is wasted. Also, the total efllciency of each motor-generator sei is very low, due to having'to design the same to be capable of taking care of the peak loads which might be imposed.

In certain installati0ris it has .been the practice to utilize an alternating current two-speed squirrel cage elevator motor. Such arrangements ha.ve proved fairly satisfactory with motors ca.-

pable of operating at suitable normal and low speeds, but this practically llmits such Installations to a motor speed ratio 015 about 3:1 between their normal and low speeds, as eflicienb alternating ourrent motors having a higher speed ratio are not usually obtainable. In high speed elevators, the low speed f the motor is too hish for satisfactory -leveling if this ratio between the motor speeds be observed, and 11 it is enlarged so as to afiord a sufllciently low leveling speed and a sufficiently high normal speed, the large number of poles requireci for the low speed winding o1 the motor results in extreme magnetic leakage and low efilciency and wouid necessitate the use of an unsuitable oversize motor. The regulation 013 motors obtainable for such purpose is very poor for higher speeds, and they, therefore, am unsuitable for high speed installations. Moreover, motors cf this type have an unsatisfactory high rate cf acceleration and retardation which becomes unpleasant particularly f.or passenger service.

Still another system which has been successfully utilized makes use o f an alternating current wound roter hoisting motor equlpped with i drive. With such control, a regulated. speed of about ten per cent 01 the full speed has been found to be satisfactory, bui; the micro-drive with its coupling arrangement and the utilization of alternating current solenold brakes constitute a costly installation having inherent objectionable operating characteristics.

In the system of the present invention, lt; is proposed to provide an arrangement embodying the most desirable featureas of the above not'ed sysiiems, and yet a system virhich mcy be more economically installed and operated.

More speciflcally, my improved system utilizes an alter'nating current hoisting motor of the slip ring or wound roter type. Practically any speed regulation can besecured w1th this type 01 motor, so that it is posslble to meet the most desirable full speed and low speed conditions of operation. For example, a regulated speed of about five to ten per cent of the 1'u11 speed is very satisfactory, and the speed 'difierences under different car loadings have been Iound to not van? greatly. It has been found, for example, that by utilizing a Counterweight equal to the weight of the elevator car plus approximately torty per cent 01 the 1u11 car load, the extreme values would be substantiaily as follows:

Regulated speed for car, Iull load. up Regulated speed for empty car, up 01' down 7 Regulated speed for car, fu 1l ioad, down 10% of full speec1 From the above, lt will be apparent that the difierences in the regulated speed under different conditiong of car loadin'g compares favorably with systems utilizing the Ward-Leonard control eliminates the disadvantages f the micro-drive, anti since any desired rate of acceleration may be utilized with the wound roter type of motor, the shocks attending the high rate of acceieration, when squirrel sage type of motors are used, are eiiminated.

Further improvements in operation have been secured by eliminating the usual alternating eurrent solenoid brake. In my improved system, the brake for the hoisting motor is 'controlled by means of a centrifugal fluid frictional device which has the characteristic of being responsive in its operation to variations in frequency. 'I'his device, which is commonly termed a Thrustor, broadly comprises a closed tank or cylinder having a piston mounted for reciprocable movement therein this piston being connected to a linkage mechanism for operating the brake shoeg against the usual closing spring. This piston carries a motor driven impeller which is adapted t0 force a fluid such as 011 from above the -piston to that portion of the cylinder below the piston. This action increases the pressure of the fiuid below the piston, with the resu1t; that the piston is forced upwardiy and the brake shoes moved in an opening direction againstthe closing spring. Deenergization of the impeller motor enables he pressure of the fluid above and below the piston to become equalized; and the brake closing spring then becomes active to restore the brake shoes to closed or braking position, and the piston of the power device is permitted 60 move t0 its normal position in the lower part of the cylinder. It will be appreciated that in such an arrangernent the actuating force of the device Will be dependent upon the frequency a1; which its motor is energized.

For normal operation in my system, means are provided Ior connecting the brake operating device motor with the stator supply 0f the hoisting motor, whereas during regulating o1 s1ovv operation of the hoisting motor the device is nonnected with a variable frequency source such as the rotor circuit of the hoisting motor, o1 the rotor of an auxiliary motor driven at a different speed than the main hoisting motor.

With the foregoing in mind, it is a primary 0bject of the herein described in\?ention to provide an improved eievator control s.vstem which may be utilized with a main alternating current hoisting motor of the wound rotor or s1ip ring type for the attainment of normal fu11 speed, regulating and leveling speeds of the elevator.

It is another object of the invention to provide an improved elevator contro1 system wherein nove1 braking mechanism is utilized for the hoisting motor and in Which the braking mechanisrn is arranged '00 be selectively connected i:o difierent energizing circuits during various operating conditions of the elevator, these circuits respectively having characteristics adapted t;o control the brake operation in a pre-determined manof full speed /2% 0f ful1 speed Was Wall as W speed elevator installations, which may be readily adjusted to secure the most clesirable accelerating, reguiating and leveling speeds ior a'particular installation, and which will a1; the same time be econornical both as t0 installation and operation.

Yet another and most importani; object oi the invention is 1:0 provide in an elevacor system improved means which will act to maintain auto matically a desired reducecl speed o1 the hoisting motor by loading the motor with a braking torque oi? such va1ue in addition the efiectiv ioad that. with Iu11 resistance in the roto1 circuit the reduced speed will be the va1ue desired.

Other objects, purposes, and advantages o1" the invention will hereinafter more fu11y appear er will be understood from the fo1lowing description of the system embodying the principies thereof which is illustrated diagrammatically in the Single figur of the accompanying drawing in association and combination With elevator apparatus in which three-phase alternating current is employed.

Elevator apparatus in geneml F01 purposes of illustrating my improved cantrol system, I have chosen to illustrate the 'sys tem as being applied to an alternating current installation in which the main apparatus ern bodies a main hoisting motor A of the siip ring or wound roter type. This motor is connected through a suitable transmission contained in the casing B for driving the usual traction sheave o1 hoisting drum C. As is the usual practice, an elevator car D is suspended in a hatchway from a hoisting cable which is passed over the traction sheave and suitable id1er pulley and con nected to the usual counterweight as shown at E. The main hoisting motor has associated With it a braking mechanisrn as generally indicated at F, and which will subsequently be described in particular. The main hoisting motor may 01' may not be connected with an a'uxiiiary motor G 01" the slip ring or wound roter type f01 a purpose hereafter to be explained.

The hoisting apparatus for each elevator rnay be mounted on a common bed p1ate so as to be positionable as a unit in the most suitabie position for performing its function.

B7akz'ng mechanism In my present system, the brake acts to maintain automaticaliy a desired reduced speed of the hoisting motor by loading the motor wit-h such a brake torque in addition to the effective motor load that the reduced speed of the Wound rotor motor, with full resistance cut in circuit, has the value desired. The alternating current soienoid brakes, as generaily heretofore used, were inherently uniit for such purpose.

As employed herein, the braking mechanism more specifically comprises, as more 01 lass diagrammatically illustrated on the drawing, a pair of brake shoes I0 which are associated With a braking drum II, each of these Shoes being associated with the usua1 toggle mechanism arranged 130 be actuated in a bral e setting direction by means' of a spring I2. In practice, I

have found it deslrable to provide t.he brate p! I:o provide the desired regulating speed or slow such size as I;o be capable o! produ'clng a bra.ke

torque o! approxi-mately 1.6 t.o 1.! times the rated motor tbrque.

F01 actuatlng the toggle mechanistn to release the brake shoes relative to the braklng drum, I have utilized a. centrifugal fluid frictlonal .device I3, commonly known a.s a Thrustor, whi ch includes In its assembly an electric motor II. The operation cf this device is well known, so that iI; ls thought that a. detailed description thereot will oe unnecessary. It may be stated, however, that when the motor H is op'erated,

power is transmitted through a. fluid medium I;o

a push rod I5 sup-ported for reciprocable movements, the amount ot power delivered to the push rod depending upon the speed or the frequency a.t which the motor I6 ls operated. In the preseni; arrangement, the push rod I5 1s counected through a suitable linkage to operate the brake toggle mechanism in a releasing directlon against the action cf the brake closing spring I2.

If the motor I I is connected to a normal 60 cycle electric circuit the bra.ke will be immediately released, and when the motor II is disconnected. the brake will be applied imme'diately. On the other band, it will be a'pparent that, if the motor II is connected to a circuitin which the frequency is being gradualiy increased 01 decreased, the brake can be so controlled as to gradually release or gradually apply the brake 'shoes to the braking drum. Advantage has been taken of these characteristics to s(acure the most; desirable braking effects during the differem; operating conditions' of the main hoisting motor, as will hereafter be explained.

Control system in general For purposes of i11ustra ting my improved Control system, the various contactors and control devices are disclosed as being arrange for A. C. operation.- I du not, however wsh to be limited in this resnect, as D. C. operating coils may be utilizedwith the various contactors withoui: e-= parting from the invention. Also, it is to be understood that. any suitable type 02 automatic starter im the main hoisting motor may Ioe utilized. and it is not necessary 120 utilize the particular arrangement disclosed in the drawing.

The system has been further illustrated as being associated with a push button control for 'the elevatbr. tro1s may be utilized. N0 attempt has been made to show a complete pusn button" control systern anti only such parts 01' the systern ate shown as are considered desirable in order to fully explain the principles of the present invention. D001 and gate contacts, safety and protective switches and the 1ike, as well as certain other parts of I;he systeui have been, omitted er only schematically represented where found desirable.

The circuit for a four-floor installation has been illustrated anti in the drawing, the eleva.tor is shown as being at the fioor level of the second floor.

The main hoisting motor has its stator counected to a main three-phase power supnly IG and is controlled as to direction of rotation by mechanlcally and electricallv interlocked up and down contactors I'I und I8 respectively. The roter or secondary of the main hoisting motor is brought out, to s1ip rings in the usual manner and connectedto external resistors I9 connected in Y. These resistors are so proportloned as speed of the motor, when all the resistance is cut in, und be of sufllclent value to assure starting with the maxlmum motor torque required. Sections cf the resistors are successively cut out by meahs of sultable accelerating'contactors 20 However, einher types of canzvator car.

lind 2I which are arranged for successive time d elay closing and instantaneous opening by the provision of sultable dash pots or otherwise.

Another pair of mechanically and electrically interlocked contactors 22 und 23 are provlded for selectively connecting the motor I4 of the braking mechanism either with the main power supply the hoisting motor o1 with the secondary circuit of the hoisting motor, when the auxiliary motor G is not being utilized. If the auxiliary motor G is being utilized, then in" stead of connecting' the motor II to the secondary of the main hoisting motor, the con nection is made to theslip rings of the auxiliary' motor. arte made through a suitable transformer 24.

F01 control by an qperator. -a plurality of push buttons 25, 25, 25. and 25 areprovided, the superscript in each case indicating the pa1ticular floor for which the push button is designated. Floor relziys 26 2B 28 and 26 are respectively provided for the difierent floors. Push buttons and floor switches may be mourited; m any suitable 1ocacioa. Within the hatchway, for eaci: floor there isprovided the usual selector direction switch. these switches, Tor the respective floors being designated ZI 2'W 21 and 21.

The selector direction switches are of the usual construction. being arranged 'as single po1e, dou ble throw switches, except for ehe first floor and t0p fioor, which are respectively retained closed in one direction only by a suitable spring. F01 the other fioors. however, the switches may be actuated int0 one position or the other by means of a suitable cam member 28 ;arried by the ele- It will be noted that when a car is at the fioor level of a particula r fioor, the se lector direction switc'n for that floor will be held in mid-position anti will thus become ineffective.

There is.also provided on the car a pair of car leveling swltches 29 and 3 which am a1- ranged to be he1d in openposition by means of associated springs, but which may be mechani cal1y actuated 1:0 closed postion by means of hatohway cams fiI and 32. In crder to prevent unnecessary and inconvenient operation of these switches, when passing non-selected floors, solenoids are provided for retaining the switches in such positi m as to be unaffected by the cams 3I and 32. II; Will be noted that With the ele vator ab the proper fl-oor level, the leveling switches will be in opened position, but the assoto the fioor. or the leveling switch 30 is held closed by the cam 32 in the event that tne elevator is moving, downwardly to the floor.

In general. the control system of the present invention provides for inital starting of the ele vator from rest under the control of the oper- In either cse, the latter connections ator,. but once the elevator has sta'rted, it will be automatically accelerated to full speecl. As the elevator approaches a. selected fioor, lt will nass into a regulating zone ab a fixed distance from the selected fioor 1evel and the control will 'automatically connect Ishe elevator hoisting motor and associated apparatus for slow speed operation and retardation until the e1evator enters a Ieveling Zone, where it will come to st op at the selected floor level. At rest at a particular floor, ehe leveling swi.tches axe arranged to be automatically actuated to maIntain the floor level, due to cable stretch changes in elevator load during loading and unloading, etc. The operation of rny control system to secure the diflerent operating conditions of the elevator will now be described in detail.

Normal operation Let it be assumed that the elevator car is disposed on the first fioor and that; it is desired to take the car to an upper floor, for example, the second floor. When the car is in the first floor position, the cam 23 retains the selector direction switch 21 in open position. so that if the push button for this floor is depressed by the operator it will have no efi5ect on the control system. Moreover, with the elevator at the first floor, the selector direction switch 21 will have been 1eft in a position thrown towardsthe right. T start the elevator, the operator pushes push button 25 which will energize the operating coil 33 of the fioor relay 25 through the following circuit: From one side of the supply circuit through the normally c1osed contacts 34 anal 35 of the main contactors I1 and I8, through comductor 36, the lower contacts of push button 25=, the operating coil 33 and thence through conductor 31 and the contacts of normally open but now closed safety devices 38 and 39 to the other side of one phase of the supply circuit. The nontacts 38 schem'atically represent; safety devices which a.re arranged to function during travel of I;he elevator but; not during leveling movements thereof, while the contacts 39 represent; safety devices such as stop buttons and the 1ike which are arranged to function at all times.

Energization of the operating coil of the floor relay 26 causes this relay to c1ose its contacts 40 und open contacts 4I, 42 and 43. Conductor 36 being connectecl With a conductor 44 to one of the contacts 40, closure of the floor relay 26 will energize the up rnain contactor I'I through the following circuit: From the energized Conductor 3G, through ehe lower contacts of push button 25, conductor 44, contacts 40, conductor 45, the right hand contact of selector direction sWitch 27", conduct;or 46, conductor 41, conductor 4fl through the normally closed contacts 49 of main contactor I8 I;o operating coi1 50 -of main contactor I1, conductor I, and thence 120 couductor 31 through contacts 39 to the other side of one phase of the supply circuit.

The main contactur I'I now c1oses to connect the stator of the hoisting motor to the power supply circuit and at the same time will close its contacts 52 to establish through conductor 53 a holding circuit for the operating coil of floor relay 26 AI: the same I:ime contacts 34 of main contactor II are opened so as to deenergize conductor 33 Ieeding the push button, I;he push buhton thus being rendered inefiectual for further operation to control the elevator until after the operation which has now been started is completed.

The hoisting mobor being now energized will start und. attain a speed determined by the secondary resistors I9 which are now all cut in. As soon a.s the contactor I'I closes, the accelerating re1a.ys 20 and 2I will have their operating coils energized through the following circuit: From one phase Wi1'e0f the power circuit through couductor 54, conductor 55 to one side of the parallel connected operating coi1s 56 and 51 of the re1ays 20 and 2I, from the other common counection of these coi1s through conductor 53, normally closed contacts 59 01 contactor 23 and thence thrcbugh conductor 50 {00 another phase wire of the motor supp1y circuit. The relays 20 and 2I are arranged to successively close at the expiration of precletermined time intervals to accelerate the hoisting motor by successively autting out sections of the resistance in 1I;s roter circuit. operation of the relay 2I acting to short;

circuit' the s1ip rings of the motor and cause II: o0 operate at full speed.

Simultaneously with the starting up of the motor, as soon as the floor relay 25 closes its contacts 40, the leveling switches 29 and 30 are energized and closed through the following circuit: From one of the contacts 40 which is now energized from one phase wire of the power circuit, through conductor GI to one side of the parallel connected operating coils 62 and 63 of the leveling switches 29 and 30, from the other common connection of these coils through conductor 64 back the other side of one phase of the supply circuit.

Closing of the contacts of the leveling switches will at this time have no efiect upon the operation.

Closing of the contacts 40 of the fl0or relay further energizes the contactor 22 through Ishe following circuit: From contacts 40, which are energized, through conductor 65, a normally closed contact; 65, conductor 61 to the operating coi1 68 01 contactor 22, conductor 89, conductor I0, and thence t0 conductors 5I and 31, and then through contacts 39 so I;he other side of the supp1y circult. Closure of contactor 22 operates to close contacs II, I2, and I3, which operatc to connect the motor I4 of the brake mechanism directly the stator circuit of the hoisting motor. Since the frequency of I:his circuit is constant, the motor I4 will operate immediately anal release the brake.

The elevator will now have been brought up to fu11 speed and will be approaching the selected floor, in this instance the second floor. After 'the initial selection of the desi:red fioor by the operator, and ir0m the time that the proper push button is manipulated, further operation o1 the e1evator is automatic.

Normal operation of the elevator in starting to go bo a lower selected fioor would Ihre the same as described above, except that the main con Isacts -of the contactor I8 would be c1osecl, the

operation of the contactor I9 being deterrnined by ehe position of the selector direction switch of the floor selected, this switch being in such position as to close 0r engage the left band comtact.

The floor relays, the leveling. relays, the cantactor 22, accelerating relays 20 anti 2I would all operate in the same manner as described above.-

Regulating operation Regul ang operzition, as considered herein, relates to the 10W speed operation of the elevator during which time all of the resistance l9 i s in the secondary or slip ring clrcuit ot the holsting motor roter. The regulating operation may theretore'take place during the retardation, unt11 the elevator 1s brought to rest at a selected floor or durlng leveling operat1'on. v

Continuing with the previously assumed movement of the elevator to the second floor, as soon 8.s the elevator reach'es a predetermined position approaching *the second floor level, such position beim; determined by the length of the cams 3I am). 28, the leveling switc h 29 which is in closed position will ride upon the cam 3I. Up I;o Ihis arrang6ment is being utilized. The connection time the switch was hold closed by t he energization of its coil 62 and will now be-held in c1osed position by the cam 3l. As the movement of the car continues, the action cf the cam 28 will operate I o operi the selector direction switch 2'IF, I:he switch assuming a, position as shown on the drawing.

2 Opening of the selector direction switch 21 interrupts I;he energizing circuit to the operating coil 50 of'the contactox I1, so that this contactor will now open its main contacts. Drop ping out of the main contactor I1 interrupts the 20 be.actuated 120 open its contacts, but the leveling switch 29 will be retained in closed position by the cam 3I. AI; the same time the contactor 22 is de-energized, so that itwill operate and disconnect the braking mechanism motor I4 from the stator circuit of the hoisting motor. II; will also be noted that when the main contactor I'I drops out, the circuit to the accelerating relays 20 and 2I is interrupted, so that these relays, which are instantaneous in opening, will have opened and inserted the entire resistance I9 into the roter circuit 0I the hoisting motorto provide s1ow speed operation, when the motor is again connected I o .the power circuit.

When the floorrelay 26 dropped out, 112 c1osed its contacts 4I, 42, and 43. The contacts 4l functi0nto connect the energized conductor 10 with the contacts of the closed leveling switch 29, so that these contacts now function to complete an energizing circuit to the operating -coil of contactor I'l thiough conductor 'I4 the contacts 43 of the floor relays, which are in series, comductor 41, conductor 48, contacts 49 the oper ating coil 50, conductor 5I and thence through conductor- 4I'and the contacts 39 to the other side of the phase of the power.circuit from which energization cf this control circuit is taken.

Thus, the main contactor I1 again 'closes, and at the same time the contactor 23 is energized from the contacts of leveling switch 29 through conductor 15, the closed contact 16 of contactor 22, conductor 'I'l, operating coil 19, and thence through conductor 69, conduotor "I0, conductor 31 and contacts 39 to complete the circ uit.

Closing of contactor 23 opens contacts 59 and prevents energization of the accelerating relays so that; the resistance I9 is entirely in circuit for slow speed operation.

The closing of contactor 23 operates to close contacts I9, 80 and 8I to 'connect the motor I4 of the braking mechanism either to the' rotor circui t of the main hoisting motor 011 to the roter circuit of the auxiliary motor G, dependof the motor I4 feed circuit is mach; through the transformer 24 so that the same motor for the braking mecihanism may be supplied by its proper voltage irrespective of whether the motor I4 is connected to the stator side of the hoisting motor .ox to a roter circuit of other voltage, which may be either the roter of the hoistini: motor or the 0 creasing frequency, which will be noted corresponds to the decreasing speed of the hoistingmotor. With this arrangement there will be 110 sudden braking, bot; the car will bo gradually reduced to the regulated speed.

As the ca.r now arrives substantially at the desired floor level, the cam 3I permits. Opening of the leveling switch 29 and the car is now ab (ehe floor level.

Opening of the switch 29 interrupts the energizing circuit to the mein contactor I'I as well as the c0ntactor 23 so that these contactors will now open to disconnect the hoisting motor und. the brake motor I4. The spring I2 o f the bra.king rr'1echanism thereupon actuates the brake to stop the car ab the floor level.

The above describes the regulating operation When approaching a selected floor from below. In approaching the selected floor from above, the operanion will similarly reduce the speed of the Gar, except that in this case it will be the cam 32 at the selected floor and the leveling switch 30 which will in this case cohtrol the operation o1 the main contactor I8 instead of contactor I'I. The contactor 23 will operate in the same manner to connect; the braking mechanism to the roter circuit.

Leveling Operation My improved system is arranged to automati- 0 wardly a slight amoun t.}below the floor level. Under these conditions, the sWitch 29 will be closed due to the act ion of cam 3I Closure of this leveling switch will energize the up main contactor I'I and the contactor 23 to connect the hoisting m'otor fc' r slow speed operation and the braking mechanism to the roter circuit in the same manner as described in connection with the regulating operation.

The elevator car will thereupon be returned tofloor level and the leveling switch 29 will open to deenergize the control devices and shut down the hoisting equipment.

A similar operation ta.kes place upon upward movement of thecar frem the floor level,

I which will be cloaed to actuate the "down" oontactor II, together wltlt the control coutactor 23 for the brate motor. 'I'he elevator ls thus returned to floor level und the control devices und hoisting motor deenerglzed.

General consideratlons The cams 2l al und 32 and the selector direction swltches at euch floor a.re so arranged in the hatchway that, when approaching a. selected floor, the leveling swltches will 'be operated by the cum 3I or ca.m 32, as the case may be, before the cum 28 operates the assoclated selected switch. Moreover, the lenzth 01 the cam 28 must be such that orte-halt of lts length is larger than the maximum stopping dlstance 01 the car wider normal speed with Iully loacled car going down or empty car going "up" und Iu1l braking torque applied.

Wlth reference to the brake operating mechanism. the bra.ke when connected to the stator side 015 the hoistlng motor will be actuated to fully released position, und when disconnected will be actuated t.o full braking positlon.

The frequency in the hoisting motor roter circuit will vary substantially lnversely as the Speed ot movement o! the rotor. That is, when the motor is operatlngat tull speed. the frequency in the roter clrcult will be substantially zero or will be proportional to the sllp. As the motor is slowed down, this frequency ls gradually increased accordlngly until with the rotor stationary, the Irequency 01 the motor clrcuit would be the sa.me as that of the stator clrcult. Since the motor II of the bra.king mechanism is responsive to frequency, advantage may be taken cf the variable frequency characterlstic of the roter circuit to secure braking efiects which vary accorcllng to the speed of the motor anti consequently the speed of the elevator. If the brake motor I4 during the regulated speed operatlon is connectecl to the roter clrcult as shown by dottecl llnes on the drawing, then the regula.tlon between the frequencx 01 the rotor clrcuit and the speed of the motor rotor will be varied in direct proportion. On the other hand, in order to secure another regulated speed, another Irequency which may-be eith er above or below that 01 the rotorfrequency of the hoistlng motor must be applied to the brake. F01 such purpbses the auxillary motor G ls utilized und the rotor of thls motor ls connected to the rotor of the main holst motor through gears cf sultable ratio to obtalu the desirecl frequency.- The auxlllary motor ls provided wlth the sa.me number of poles as the maln slip r'lng motor, und since the auxiliary motor will act a.s a. frequency changer to feecl the motor I4, the auxlliary motor may be of relatlvely small slze.

With the above manner of energlzlng the mo tor H, the voltage of the roter circult, irrespective of whether this clrcult ls froxn the rotor of the maln hoistlng motor or the a.uxlliary motor G, will change in the same proportlon as the rotorfrequency applied to the clroult. Therefore, the brake motor operates electrically in the entlre range from zero to full frequency and full voltage under rated condltions.

By connecting the rotor of the auxiliary mtor so that ltls drlven Irom the maln holstlng motor al; one-hallf speed, lt wlll be apparent ths.t the trequency in the roter circult of the a.uxlllary motor wlll be 30 cycles when. the Ireexcept um: m um case lt m the levellng man quency 01 the roter clrcuit o! the man: holstln: motor would be auhatv.ntln.lly zero, where the maln power supply ilot 0 cycle character. On the other band, lt the "lluxillary motor is drlven at twlce the speed o! the hoistina motor, the trequency ln the auxlllary motor rotor circuit will have been reduced to zero whe'n the maln holst motoris operatlng at 50 per cent speed.

From the Ioregoi ng lt will be noted that the rate o! chanse in the Irequencywhen going lrom tul1 speed o! the holstlng motor to slow speed may be varled clepending upon whether the a.uxlliary motor is driven at a greater or lesser speed than the holstlng motor, or whether the motor II is energlzed from the rotor circuit o! the hoistlng motor. O! course. the rate o! chanze ln the Irequency will likewlse cha.nge the braklng eflect obta.lnable on the hoistillli motor. It is therefore posslble to obtain the most desirable braklng eflect Ior the partlcular regulated speed whlch ls to be used.

From the foregolng desoription lt will be appaierit that the present inventlon provldea an lmproved eleva.tor control system which may be utilized with a main alte'rnatlng current holsting motor o! the wound roter type for the attainment ot normal fu1l speed, regulatied und leveling spegds of the elevator; which embodies an improved braking mechanlsm on the holst- -lng motor, thls braklng mechanlsm belng arranged to be selectlvely connected to difierent energizing clrcults for various operating conditions of the elevator, these clrcults having characterlstics adapted to control the bra.ke operation in a predetermined manner most sultable for a. partlcular condltlon of elevator operatlon; a system which ma.y be reaclily adapted for all automatlcally controlled elevators, which is sufilciently flexible to permll; of lts use with high speed, as well as slow speed eleva.tor lnstallatlon, which may be readlly adlusted. to secure the most deslrable accelera.tlng, regulated und leveling speeds for a particular installatlon, und which will at the sa.me tlme be economical both as to installatlon und operation.

It is, of course, to be understood that although I have descrlbecl in detail a. preferred embodlment of my inventlon, the inventlon is not to be thus llmlted but only insoi'ar as defl ned by the scope anti spirit of the appended claims.

I clalm as'my inventlon:

1. In an elevator control system the comblnatlon comprlsing, load elevatlng -anci lowerlng means, a, hoistlng motorthenfor of the aliprlng type, electro-responsive devlcs Ior coutrolllng sa.id motor, braking mea.ns for sa.id motor actuata.ble ln response to Irequency changes in a. slngle energlzlng clrcuit therefor, und means selectively operable under diflerent 'operatlnz condltlons o! sald first means to energize sa.ld circuit from the prlxnary side ot sald motor und from the secondary slde 01 the motor.

2. In an elevp.tor control system the combina.tlom comprislng, load elevatlng und lowerlnz mea.ns an alternatlng current holsting motor therefor, electro-responsive devices l'or controlllng sali'l motor, an auxillary motor of the sllpring type ha.vlng lts rot0r mechanically coupled wlth the holsting motor throuzh a speed changing devlce a.nd its primary electrically paralleled with th e hoistlng motor primary, braklng means for sald motor actuatable in response to frequency ohanges in am energlzing circult therefor, und man: selectlvely operable under dilferent; operating conditions for energizing said circui t from the primary-side cf said motors am! l the secondary side of the auxiliary motor.

3. In combination; an elevator car adapted to serve aplurality of landings; a hoisting motor theret'or, a source of current for the motor, a 'frequency responsiye brake for said motor. means for initiating opetation of said motor und simultaneously completely releasing said brake, means operablev upon the arrival of said car at a certa.ln dlstance from a landing at which a stop is to be made to connect the motor for slow speed operatlon and apply the brake, am! means for applying to said brake a frequancy variable In accordance with the motqr speed to gradually release the braking effect as the motor speed is reduced.

4. In combination; an elevator car adapted to serve a plurallty oflandings; a holstlng motor therefor 015 the wound-roter type; a source of current for the motor, a frequency responsive brakia for sald motor having'an energizing circult, means for causlng connection of t.he motor and said energizlng clrcuit of said brake directly to sa.id source 170 completely release the brake a.nd simultaneously start the motor, means operab1e upon t;he arrival o1 the car at a certain distance from a landlng at which a st.op is to be made to connect 'the motor for slow speed operation am! apply the brake, and means for disconnecting sald energizlng circuit cf said brake from said sou1ce and for connecting sald energizing circuit of the brake to the variable frequency of the motor roter to gxadually release the brakingefiect as the motor speed is reduced.

5. In combintion: an elevator car adapted to serve a plurality of laxidings; a hoisting motor therefor of the wound-rotor typea source of eurrent fo r the motor, a. frequency responsive brake for said motor, said brake having a single energizing clrcuit, means for causing connectlor': of the motor and the energlzing.circuit ot sa1d brake to said source to release the'brake and start the m'otor and mechanlsm for automatically stopplng the car at a deslred landing, said mechanism comprising means controlled by the car movemotor, said brake having a single energizing circuit therefor, means lncludlng a leveling clrcuit for connecting und selectively energlzing the motor for Operation in opposlte dlrections at slow speed arid connecting said energizing clrcuit of said brake with the roter circuit of the m otor,

said means being de-energized when the car is Y at a floor level, means responsive to car m ovments for controlling sald circuit to automatically retum the car to floor level, when the car ls moved away therefrom, and manually cc'mtrolled means for rende'ilng said latter mean's ineflectual,

- ing primary and secondary circuits, braking means for said motor lncludinga second lnduction motor for releasing said brakes, said second motor having a primary windlng am! a secondary winding, and means operable under dlflerent nperating conditions for selectively connectlng one of said windings only to the primary clrcuit o1 said first niotor and to the secondary clrcuit of said flrst motor.

8. In an elevator control system the combination comprising, a load elevatlng ahd lowering means a wound roter lnductlon motor for elevating and lowerlng sald means, sald motor having primary and secondary circults; bral;ing

ment for connecting the motor for a pre-determlned slow speed operation a1: a fixed. distance from said source and said brake from said roter at a fixed distance nearer the landing to apply the brake and stop the muten m combination, an elevator car, an alternaeing current: variable speefi hoistlng motor therefor, a frequency respunsive brake for said means for said motor includins a second induction motor for releasing said b rakes said second motor having a stator clrcuit am! a roter clrcuit and means operable under d;lfl'erent operating condition for selectively conn'ectlng said stator 015 said seconc l motor bo the prlmary clrcu; 01 sa1d flfst motor and to the secondary circuit thereof.

9. In an elevatoncontrol system, the combinat1on comprising a load elevating and Iowerlng means, a wound roter inductlon motor for elevatlng and lowering said means, an auxfliary mot.or o f the slip ring type having its roter mechanically coupled with am! driven by said flrst motor through a, speed changing device, said auxiliary motor having its primary electrically connected in parallels with the primary of said first motor, braking mean s for sald flrst motor including a third induction motor for releasing said brakes, and means selectlvely operable under different operating conditions for energizing. the

primary of said. third motor from the primary of said flrsi'. motor and from the secondary 02 said sec0nd muten ERNST L. SCHWARZ. 

